1. Field of the Invention
The present invention relates to a backlight module, and more particularly, to a side-edge type backlight module.
2. Description of Related Art
With reference FIG. 1, which is a cross-sectional view of a conventional liquid crystal display device, the conventional liquid crystal display device comprises: a back plate 11, a light emitting diode light bar 12, a light guide plate 13 and a reflective sheet 14. The reflective sheet 14 is located between the light guide plate 13 and the back plate 11. The back plate 11 encloses the light emitting diode light bar 12, a light guide plate 13 and the reflective sheet 14 therein. Besides, the back plate 11 includes a bottom plate (not shown in the figure) and a side wall 111 protruding upwardly from the periphery of the bottom plate (not shown in the figure). The aforementioned light emitting diode light bar 12 is fixed on the side wall 111. Moreover, the conventional liquid crystal display device further comprises an optical film set 15 located above the light guide plate 13, for modulating the light emitting upwardly from the light guide plate 13.
After the conventional liquid crystal display device is completely assembled, a liquid crystal display panel 16 is located on the optical film set 15, wherein an upper frame 17 covers the aforementioned liquid crystal display panel 16 and the back plate 11. Besides, the side wall 171 of the upper frame 17 is fixed to the side wall 111 of the back plate 11, wherein the aforementioned elements of the conventional liquid crystal display device are fixed inside the back plate 11.
However, when the conventional liquid crystal display device is operated, the heat produced by the light emitting diode light bar 12 having plural light emitting diodes 121 is continuously transmitted to the side wall 111 of the back plate 11. Moreover, the heat is not only transmitted to the whole part of the back plate 11, but also transmitted upwardly to the reflective sheet 14 being in contact with the back plate 11. As a result, the temperature of the reflective sheet 14, the light guide plate 13, and the optical film set 15 increases gradually. The optical properties of these three elements vary with the increasing temperature. Therefore, the light guide plate 13 and the optical film set 15 will have warped deformation. Besides, the transmittivity and the responding speed of the liquid crystal on the liquid crystal display panel 16 will also deteriorate with time. That is, after long-term operation, the display properties of the conventional liquid crystal display device will be impaired.
Therefore, it is desirable to provide a backlight module which can prevent the heat produced by the light emitting unit being transmitted to the optical elements of the backlight module.